The long term objective of our research is to better understand the mechanisms underlying both normal and abnormal vestibulo-ocular function. The aim of the present proposal is to develop new ways of testing and analyzing the vestibulo-ocular reflex (VOR). The research strategy is to make quantitative measurements of vestibulo-ocular function in humans using paradigms suggested by the results of both recent neurophysiological studies as well as mathematical analyses of VOR function. In particular, we will choose rotational vestibular and optokinetic stimuli that exceed the capabilities of or circumvent the compensatory mechanisms which normally make vestibular diagnosis so difficult. We will begin by applying the new methodology to the detection of unilateral peripheral vestibular disease (UPVD) -- first in patients with complete loss, then those with partial loss -- with the ultimate plan to extend our results to patients with central vestibular disorders. We plan to 1) use brief, high-velocity head-on-body movements to expose UPVD, 2) determine (with the magnetic field search coil technique) if inappropriate directly slow phase eye movements during high-velocity vertical or horizontal head rotations are a reliable index to UPVD, 3) develop a new test to measure vertical semicircular canal function by using their contribution to the horizontal (eye in head) VOR, 4) use the initial slow phase velocity profile (plateau effect), in response to a constant velocity head rotation, to detect UPVD and 5) examine the usefulness of optokinetic afternystagmus (OKAN) in assessment of UPVD. Our results will provide new information useful in the assessment of the large number of patients with nystagmus, visual blurring and oscillopsia, and vertigo and dizziness.